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SUMMARYSeed cotton yield in Northern Cameroon has been declining since the 80s despite breeding efforts. In order to evaluate the impact of genetic improvement on this decline, we conducted field experiments in two locations with 10 widely grown cotton cultivars released in Cameroon between 1950 and 2009. The rate of genetic gain (GG) was estimated with a linear regression of the cultivar mean on its year of release (YR). Contrasts between rates of GG observed with different planting dates were estimated and tested. Our results revealed a rate of GG on fibre yield of 3.3 kg ha−1 year−1 due to increased ginning out-turn (3.9% and 6.2% in 60 years in Garoua and Maroua, respectively). There was no GG on leaf area index (LAI), radiation use efficiency (RUE), aerial biomass, harvest index and on seed cotton yield. We concluded that cotton breeding efforts in Cameroon have successfully improved cotton fibre yield but there is still some room for seed cotton yield improvement.

Rainfed crop production predominates in West Africa. Rice is an important staple food, especially in Senegal. The scope for increase in rice production under irrigated conditions is uncertain. Rainfed rice is therefore a key component for regional food security impelling agronomists to assess climate change impact on rainfed rice yield and to design rainfed rice ideotypes suited to future climate scenarios. The DSSAT CSM-CERES-Rice model was thus calibrated and evaluated on 19 agronomic experiments conducted in 2012, 2013, and 2014, in 6 locations, with 21 cultivars and two fertilization levels (20 and 80 kg N ha −1 ). Simulations were then carried out with the crop model forced with the downscaled projections of seven climate models, with and without considering the impact of an increase in atmospheric [CO 2 ], using an ensemble of global circulation models and two Representative Concentration Pathways (RCP2.6 and RCP8.5). Simulated rice yield was divided by two over the century with RCP8.5 and stagnated with RCP2.6. Elevated [CO 2 ] significantly increased yields, but this effect could not offset the yield decline due to elevated temperatures. Cultivars with longer vegetative phases and greater temperature tolerance were better adapted to climate change than current cultivars. Using these new cultivars with the recommended fertilization rate (80 kg N ha −1 ) could offset the yield decline due to climate change. For the first time, we bring together a study based on a process-based crop model handling crop response to elevated [CO 2 ], a large set of field experiments and up-to-date climate projections (i) to provide useful insights into plausible impacts of climate change on rainfed rice in Senegal and (ii) to identify cultivar characteristics relevant for adaptation to future possible climates. Our findings will help set priorities for breeding resilient cultivar in the region.

With increasing production costs in the southeastern US, cropping systems that improve agronomic and economic sustainability are critical. A sod‐based system utilizing a two year rotation of establishing and grazing bahiagrass (Paspalum notatum Flueggé) followed by a year of peanut (Arachis hypogaea L.) and a year of cotton (Gossypium hirsutum L.) was established in Marianna, FL. The effect of grazing in this system on root dimensions (length, diameter, and surface area) of cotton was monitored using a mini‐rhizotron technique. There were differences in several root parameters between grazed and non‐grazed plots (256 m2) including: cotton root length (1260 mm grazed vs. 844 mm non‐grazed), surface area (1727 mm2 grazed vs. 1105 mm2 non‐grazed), and diameter (3.09 mm grazed vs. 2.51 mm non‐grazed). The roots in the 15 to 30‐cm‐depth profile had greater length and surface area in the grazed plots with the greatest root surface areas in the deepest soil profile (75‐90 cm). Grazed plots also exceeded non‐grazed plots in seed cotton yield (3967 kg/ha vs. 3335 kg/ha) and lint (1672 kg/ha vs. 1444 kg/ha). Increases in root architecture associated with cattle grazing in this system may enable cotton to better withstand adverse environmental conditions such as drought stress, thereby improving long‐term sustainability.